Lecture 5 - Keyboard Scanning and De-Bouncing

Lecture 5 - Keyboard Scanning and De-Bouncing

1. Keyboard Scanning

   • Example: Pressing D Button on Keyboard
     • Connects Column1 to Row2
       • Select C0, Check R0-R3
         • If a switch is closed, then key on the switch is pressed
         • If R0-R3 Switches are all open, then switch pressed on C0
           • Iterate through remaining Columns checking each row, still closed switch is closed
   • Used to identify which key is pressed
   • Pullup Resistors used to hold Row lines high when no buttons are pressed
   • Resistors in series with each column line to prevent damage to the circuitry if two buttons are pressed at the same time

2. Key Debouncing

   • Contact Bounce Problems
     • When mechanical switches are closed, the contacts bounce instead of resting instantly
       • Generates a series of pulses
     • When the computer is faster than the switch, each pulse will be registered as a new input
   • Software Debouncing
     • Put a delay in the code, after keypress detected

3. Switch Debouncing

   • Each software or hardware techniques can be used to debounce switches

4. 7-Segment Display

   • Common Cathode or Common Anode
   • Each Segment has a pin
   • BusOut API used to group all outputs into one
     • LSB to MSB